Patients suffering metabolic diseases, such as diabetes, are rapidly increasing due to the recent rich and varied diet. Intake of excessive nutrients induces oversecretion of insulin to cause indirectly a metabolic unbalance, thus leading to glucose intolerance (hyperglycemia), diabetes, hyperlipemia, arteriosclerosis, etc. Diabetic patients in particular suffer insufficient insulin function and glucose intolerance so that their blood glucose level drastically increases after meals to invite complications such as damages in blood capillaries and arteriosclerosis.
It is thought effective for prevention and treatment of such diseases to take in medications or foods that will depress the rise of blood glucose level after intake of essential nutrients or that will inhibit excessive secretion of insulin. Therefore a substance capable of controlling or inhibiting the hydrolysis of ingested starch into glucose and a substance capable of controlling the insulin secretion are demanded.
From the above aspects, various studies have been made on amylase inhibitors that inhibit an activity of an amylase from hydrolyzing starch into glucose. Since the report that wheat contains the amylase inhibitor, the research and development of the amylase inhibitors of wheat origin have been carried out.
The wheat-origin amylase inhibitors include 0.19 AI (AI: amylase inhibitor), a protein constructed of two subunits each consisting of 124 amino acid residues and having the molecular weight 13,337, in which a single band is observed at the mobility 0.19 by polyacrylamide gel electrophoresis (Swiss Port: ID=IAA1_WHEAT); 0.28 AI, a protein constructed of two subunits each consisting of 123 amino acid residues and having the molecular weight 13,326, in which a single band is observed at the mobility 0.28 by polyacrylamide gel electrophoresis (U.S. Pat. No. 5,444,046, Swiss Port: ID=IAA2_WHEAT); and a protein constructed of two subunits each consisting of 124 amino acid residues and having the molecular weight 13,185, in which a single band is observed at the mobility 0.53 by polyacrylamide gel electrophoresis (U.S. Pat. No. 5,726,291, Swiss Port: ID=IAA5_WHEAT). These amylase inhibitors are known to be effective in inhibiting the rise in the blood glucose level and controlling the insulin secretion. The mobility according to the polyacrylamide gel electrophoresis is based on the mobility 1 of bromphenol phenol according to the polyacrylamide gel electrophoresis (7.5%, pH 9.5), as described in J Sci. Food Agric., 20, pp. 260-261 (1969).
JP-A-46(1971)/1833 and JP-A-61(1986)/171431 disclose that the amylase inhibitors extracted from wheat with water, an acid or an aqueous alcohol may be used in treatments of diabetes and obesity. However, these conventional amylase inhibitors of wheat origin do not produce as much results as expected when orally administered to humans; they can achieve only a limited effect of inhibiting the digestion (hydrolysis) of heat cooked starch, such as of cooked rice, into glucose and are expensive.
U.S. Pat. No. 5,332,803 discloses a process for the preparation of amylase inhibitor, which comprises the steps of extracting wheat, wheat flour or wheat gluten with water, an acidic aqueous solution, an alkali aqueous solution or an aqueous alcohol to produce an extract solution (the solution may be otherwise a starch wastewater discharged in the process of recovery of starch from wheat flour, etc.); adding a polysaccharide, such as sodium alginate, to the extract solution to form an insoluble complex; recovering the complex from the solution and dissolving or dispersing it in a solvent; dissociating the polysaccharide from the complex and removing it from the solution; treating the resultant solution with a cation exchange resin; and recovering the amylase inhibitor from the fractions passed through the cation exchange resin. The amylase inhibitor produced by the above process shows a very high inhibitory activity against the amylase but hardly against trypsin. The amylase inhibitor also has a high inhibitory activity against the amylase contained in pancreatic juice so that it is very effective in controlling the insulin secretion.
The method of JP-A-7 (1995)/48268 is capable of treating a large amount of materials with good operability while reducing wastes so that the mass production of the objective amylase inhibitor can be obtained. The method, which also uses the above amylase inhibitor-containing solution (of the U.S. Pat. No. 5,332,803) obtained by removing from the liquid the polysaccharide dissociated from the insoluble complex of the amylase inhibitor and the polysaccharide, comprises the steps of precipitating 40-70% of the protein contained in the solution; dissolving the precipitated protein in water to prepare another solution containing the amylase inhibitor; adding calcium and phosphoric ions to the newly obtained solution to insolubilize a complex containing the amylase inhibitor and recovering it from the solution; and solubilizing the amylase inhibitor of the insolubilized complex in water to obtain a solution containing the amylase inhibitor. The resulting final product contains the amylase inhibitor in high concentration and has a stronger amylase inhibitory activity.
According to the methods disclosed in U.S. Pat. No. 5,332,803 and JP-A-7(1995)/48268, the obtainable amylase inhibitors contain in high concentrations 0.19 AI that has a very high inhibitory activity against the amylase but not against or hardly against trypsin. The amylase inhibitors obtained by these methods are highly inhibitive against the amylase contained in pancreatic juice and are therefore effective in controlling the insulin secretion. Accordingly those amylase inhibitors can be an effective suppressant for the hydrolysis of heat cooked starch, such as of cooked rice, into glucose.
However, the method of U.S. Pat. No. 5,332,803 involves the use of cation exchange resin, which necessitates washing of the cation exchange resin after preparation of the amylase inhibitor so that it can be reused. The process of JP-A-7(1995)/48268 comprises so many steps that it is complicated. Thus, the advent of a simpler and more efficient process capable of quick production of the amylase inhibitor with good productivity is demanded.
It is accordingly an object of the present invention to provide a process for the preparation of amylase inhibitor, the process being simple and productive so that the amylase inhibitor containing in high concentrations 0.19 AI that is highly inhibitive against the amylase can be obtained quickly and in high yields.